The present invention relates to reducing the jet noise from a bypass turbomachine nozzle. The invention relates more precisely to a bypass turbomachine with reduced jet noise.
Nowadays, sound pollution has become one of the major concerns of engine manufacturers, since they are becoming ever more confronted with the noise nuisance produced by their turbomachines. The sources of noise in a turbomachine are numerous, however it has been found that the jet noise at the outlet from the nozzle is the predominant noise, particularly while an airplane is taking off.
Certification authorities are becoming more and more demanding concerning noise emissions from turbomachines, and engine manufacturers are being required to reduce the noise produced by their turbomachines, and in particular the jet noise at the nozzle outlet.
Typically, a bypass turbomachine has a fan driven by a gas generator, a primary annular channel for passing a primary gas stream coming from the gas generator, said primary channel being defined on the outside by a primary fairing, and a secondary annular channel for the fan that passes a secondary stream of gas from the fan, the secondary channel being disposed coaxially about the primary channel and being defined on the outside by a nacelle.
In such a turbomachine, the jet noise comes essentially from the primary and secondary gas streams mixing in shear and from the secondary gas stream mixing in shear with an outer stream of air going round the nacelle. This noise is broadband noise at frequencies that are generated by two types of sound source: high frequency noise coming from small turbulent mixing structures between the generated streams close to the nozzle; and low frequency noise coming from large turbulent structures that appear far away from the jet.
Various solutions have been devised to reduce jet noise at the nozzle outlet. Those solutions are based on the principle of increasing mixing between the gas streams.
One of the known solutions consists in providing the turbomachine with a plurality of repeated patterns that are distributed all around the circumference of the trailing edge of the primary fairing and/or of the nacelle. By putting such patterns into place, mixing between the streams takes place by creating turbulence (or vortices) close to the nozzle so as to dissipate kinetic energy better, and consequently reduce the turbulent intensity of the large vortices that constitute the major sources of noise. By way of example, reference can be made to the following publications: U.S. Pat. No. 6,532,729 and US 2002/0164549-A1.
Another known solution consists in taking off air from within the turbomachine and injecting it through the trailing edge of the primary fairing and/or of the nacelle. Blowing air in this way also serves to encourage mixing between the streams by creating turbulence close to the nozzle so as to dissipate kinetic energy better. Reference can be made for example to the following publications: EP 1 580 417 and EP 1 580 418.
The present invention seeks to provide such a solution for reducing jet noise by blowing air, and to install it in a turbomachine having a thrust reverser system of the grid type.
In order to implement a grid type thrust reverser system, the nacelle has two thrust reverser covers in its downstream portion, which covers are in the form of semicylinders capable of sliding in a downstream direction parallel to the longitudinal axis of the turbomachine.
Unfortunately, the presence of these longitudinally-movable covers manifestly raises a problem of conveying air from the point where it is taken off in the turbomachine all the way to the trailing edge of the nacelle from which the air is to be blown. The air delivery circuit necessarily passes via the thrust reverser covers, so it must be able to accommodate their ability to move.
Furthermore, when the nacelle of such a turbomachine also includes two maintenance covers in its central portion that are suitable for pivoting about hinges that are parallel to the longitudinal axis of the turbomachine, the circuit for delivering the air that has been taken off is even more complicated to provide.